HTT and spinocerebellar ataxia type 1: In addition to huntingtin, expansion of polyQ-encoding CAG repeats in several genes have also been found in other polyQ repeat diseases, such as Ataxin-1 in spinocerebellar ataxia type 1 (SCA1), Ataxin-2 in SCA2, Atantin-3 in SCA3, α1A-voltage-dependent calcium channel (CACNA1A) in SCA6, Ataxin-7 in SCA7, Atrophin-1 in dentatorubral-pallidoluysian atrophy (DRPLA), and androgen receptor in SBMA (Zoghbi and Orr, 2000; Del Cano-Espinel et al., 2015).